Prefabricated reinforcements that are used for embedding in masonry wall bed joints (also known as “bed joint reinforcements”) and which are intended to improve the mechanical performance of walls, consist of two longitudinal steel bars or plates connected at given distances by other transverse bars or plates, or by a continuous plate forming a triangular lattice.
The joint reinforcements currently on the market come in various geometrical configurations, but their geometry always remains constant throughout the piece, keeping the same position, even at the ends.
Thus, for example, the applicant's GEOFOR® standard reinforcement belongs to the triangular lattice group. The unique characteristic of this arrangement is that the reinforcement cannot be deformed on its plane. This provides a crucial advantage for the component's mechanical performance by making it resistant to perpendicular forces from the wall along its plane, regardless of the contribution of the mortar in which it is embedded.
This unique characteristic of reinforcements with triangular lattice shapes remains the same across the entire piece up to the joints at the ends which represent the first and last triangulation. Conversely, in the case of the ends of parts made up of segments of non-triangular bars, their capacity to transmit forces to the system as a whole depends on the mortar that surrounds them. Precisely at the ends of the pieces, and only at their ends, it is necessary for there to be mortar that is properly covered in order to prevent the system from deforming, and to transmit the forces along the length of the wall.
When reinforcements are assigned a structural role in order to increase the mechanical properties of the wall in which they are installed, the possibility of transmitting forces is entrusted to the overlaps of each component they border. Therefore, the end conditions are particularly designed for this purpose. On the other hand, the bars are cut after the steel wire is galvanized, so that the ends of the parts' cut sections are left without proper protection.
As for the overlaps of the reinforcements, it is not possible to superimpose them vertically because the dimensions established for their thickness do not provide for the possibility of properly coating the bars with a suitable mortar that would make it possible to transmit the forces. Therefore, the overlapping is installed along the same plane, connected to the end of a contiguous component.
In addition to a decrease in the performance of the overlapping reinforcement, the overlapping process also entails a series of drawbacks:
1. The need to manipulate the components on site. In order for the overlap to have the minimum required length (around 250 mm), shears need to be used to make at least one diagonal cut at the end of each piece. The cut sections, in turn, represent new unprotected points that run the risk of corrosion.
2. Decrease in the mortar covering. The set of overlapping bars must be covered with enough mortar between them to properly transmit the forces for which they are designed. This entails a decrease in the nominal covering in comparison to the lateral edge of the wall around the overlap areas. The problem is exacerbated because it is precisely at the overlap areas where the cut sections of the reinforcements lie—where the steel is unprotected. It is important to note here that if the wall reinforcement is protected, it is sufficient to have a 15 mm lateral covering, but if bare steel is used, then standards require a minimum covering of 30 mm from any point on the edge of the wall's exterior.
3. Decreased resistance in the wall. In order to adhere to the minimum coverage specified by standards as a protection requirement, the lateral edges of wall reinforcements in overlapping areas must have narrower reinforcement than what would be viable in a center area. This entails a proportional decrease in the reinforced wall's resistance to lateral forces.
4. The impracticality of meeting the minimum covering requirement in hollow reinforcement assemblies. In hollow reinforcement assemblies the reinforcement must have a minimum width in order to be housed in the external band of the mortar. This situation is incompatible with the minimum coating requirement for reinforcements in overlap areas.
The difficulty in simultaneously meeting the requirements for length and overlap covering in reinforcement overlaps, combined with the geometry and dimensions of the masonry components in use restricts the possibility of assigning structural tasks to the wall reinforcement, and this substantially decreases the manufacturer's conditions for protecting the system from external exposure.